/*
 * tsh - A tiny shell program with job control
 *
 * Harbin Institute of Technology 1603002 1150810613 Qiuhao Li
 *
 * Anyone can modify this code and then redistribute it to help others.
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>

/* Misc manifest constants */
#define MAXLINE    1024   /* max line size */
#define MAXARGS     128   /* max args on a command line */
#define MAXJOBS      16   /* max jobs at any point in time */
#define MAXJID    1<<16   /* max job ID */

/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1    /* running in foreground */
#define BG 2    /* running in background */
#define ST 3    /* stopped */

/*
 * Jobs states: FG (foreground), BG (background), ST (stopped)
 * Job state transitions and enabling actions:
 *     FG -> ST  : ctrl-z
 *     ST -> FG  : fg command
 *     ST -> BG  : bg command
 *     BG -> FG  : fg command
 * At most 1 job can be in the FG state.
 */

/* Global variables */
extern char **environ;      /* defined in libc */
char prompt[] = "tsh> ";    /* command line prompt (DO NOT CHANGE) */
int verbose = 0;            /* if true, print additional output */
int nextjid = 1;            /* next job ID to allocate */
char sbuf[MAXLINE];         /* for composing sprintf messages */

volatile pid_t fg_pid;
volatile sig_atomic_t fg_pid_reap;
pid_t stopped_resume_child;

struct job_t {              /* The job struct */
    pid_t pid;              /* job PID */
    int jid;                /* job ID [1, 2, ...] */
    int state;              /* UNDEF, BG, FG, or ST */
    char cmdline[MAXLINE];  /* command line */
};
struct job_t jobs[MAXJOBS]; /* The job list */
/* End global variables */


/* Function prototypes */

/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv, char *cmdline);
void do_bgfg(char **argv, char *cmdline);
void waitfg(pid_t pid);

void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);

/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv);
void sigquit_handler(int sig);

void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int maxjid(struct job_t *jobs);
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
int deletejob(struct job_t *jobs, pid_t pid);
pid_t fgpid(struct job_t *jobs);
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid);
int pid2jid(pid_t pid);
void listjobs(struct job_t *jobs);

void usage(void);
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);

/*
 * main - The shell's main routine
 */
int main(int argc, char **argv)
{
    char c;
    char cmdline[MAXLINE];
    int emit_prompt = 1; /* emit prompt (default) */

    /* Redirect stderr to stdout (so that driver will get all output
     * on the pipe connected to stdout) */
    dup2(1, 2);

    /* Parse the command line */
    while ((c = getopt(argc, argv, "hvp")) != EOF) {
        switch (c) {
        case 'h':             /* print help message */
            usage();
        break;
        case 'v':             /* emit additional diagnostic info */
            verbose = 1;
        break;
        case 'p':             /* don't print a prompt */
            emit_prompt = 0;  /* handy for automatic testing */
        break;
    default:
            usage();
    }
    }

    /* Install the signal handlers */

    /* These are the ones you will need to implement */
    Signal(SIGINT,  sigint_handler);   /* ctrl-c */
    Signal(SIGTSTP, sigtstp_handler);  /* ctrl-z */
    Signal(SIGCHLD, sigchld_handler);  /* Terminated or stopped child */

    /* This one provides a clean way to kill the shell */
    Signal(SIGQUIT, sigquit_handler);

    /* Initialize the job list */

    initjobs(jobs); /* don't need to protect jobs */

    /* Execute the shell's read/eval loop */
    while (1) {

    /* Read command line */
    if (emit_prompt) {
        printf("%s", prompt);
        fflush(stdout);
    }
    if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
        app_error("fgets error");
    if (feof(stdin)) { /* End of file (ctrl-d) */
        fflush(stdout);
        exit(0);
    }

    /* Evaluate the command line */
    eval(cmdline);
    fflush(stdout);
    fflush(stdout);
    }

    exit(0); /* control never reaches here */
}

/*
 * eval - Evaluate the command line that the user has just typed in
 *
 * If the user has requested a built-in command (quit, jobs, bg or fg)
 * then execute it immediately. Otherwise, fork a child process and
 * run the job in the context of the child. If the job is running in
 * the foreground, wait for it to terminate and then return.  Note:
 * each child process must have a unique process group ID so that our
 * background children don't receive SIGINT (SIGTSTP) from the kernel
 * when we type ctrl-c (ctrl-z) at the keyboard.
 */
void eval(char *cmdline)
{
    char *argv[MAXARGS];
    int bg_flag;

    bg_flag = parseline(cmdline, argv); /* true if the user has requested a BG job, false if the user has requested a FG job. */

    if (builtin_cmd(argv, cmdline)) /* built-in command */
    {
        return;
    }
    else /* program (file) */
    {
        if (access(argv[0], F_OK)) /* do not fork and addset! */
        {
            fprintf(stderr, "%s: Command not found\n", argv[0]);
            return;
        }

        pid_t pid;
        sigset_t mask, prev;
        sigemptyset(&mask);
        sigaddset(&mask, SIGCHLD);
        sigprocmask(SIG_BLOCK, &mask, &prev); /* block SIG_CHLD */

        if ((pid=fork()) == 0) /* child */
        {
            sigprocmask(SIG_SETMASK, &prev, NULL); /* unblock SIG_CHLD */

        	
            if (!setpgid(0, 0))
            {
            	dup2(STDIN_FILENO,0);
            	dup2(STDOUT_FILENO,1);
                if (execve(argv[0], argv, environ))
                {
                    fprintf(stderr, "%s: Failed to execve\n", argv[0]);
                    _exit(1);
                }
                /* context changed */
            }

            else
            {
                fprintf(stderr, "Failed to invoke setpgid(0, 0)\n");
                _exit(1);
            }
        }
        else if (pid > 0)/* tsh */
        {
            if (!bg_flag) /* exec foreground */
            {
                fg_pid = pid;
                fg_pid_reap = 0;
                addjob(jobs, pid, FG, cmdline);
                sigprocmask(SIG_SETMASK, &prev, NULL); /* unblock SIG_CHLD */
                waitfg(pid);
            }
            else /* exec background */
            {
                addjob(jobs, pid, BG, cmdline);
                sigprocmask(SIG_SETMASK, &prev, NULL); /* unblock SIG_CHLD */
                printf("[%d] (%d) %s", maxjid(jobs), pid, cmdline);
            }
            return;
        }
        else
        {
            unix_error("Failed to fork child");
        }
    }
    return;
}

/*
 * parseline - Parse the command line and build the argv array.
 *
 * Characters enclosed in single quotes are treated as a single
 * argument.  Return true if the user has requested a BG job, false if
 * the user has requested a FG job.
 */
int parseline(const char *cmdline, char **argv)
{
    static char array[MAXLINE]; /* holds local copy of command line */
    char *buf = array;          /* ptr that traverses command line */
    char *delim;                /* points to first space delimiter */
    int argc;                   /* number of args */
    int bg;                     /* background job? */

    strcpy(buf, cmdline);
    buf[strlen(buf)-1] = ' ';  /* replace trailing '\n' with space */
    while (*buf && (*buf == ' ')) /* ignore leading spaces */
    buf++;

    /* Build the argv list */
    argc = 0;
    if (*buf == '\'') {
    buf++;
    delim = strchr(buf, '\'');
    }
    else {
    delim = strchr(buf, ' ');
    }

    while (delim) {
    argv[argc++] = buf;
    *delim = '\0';
    buf = delim + 1;
    while (*buf && (*buf == ' ')) /* ignore spaces */
           buf++;

    if (*buf == '\'') {
        buf++;
        delim = strchr(buf, '\'');
    }
    else {
        delim = strchr(buf, ' ');
    }
    }
    argv[argc] = NULL;

    if (argc == 0)  /* ignore blank line */
    return 1;

    /* should the job run in the background? */
    if ((bg = (*argv[argc-1] == '&')) != 0) {
    argv[--argc] = NULL;
    }
    return bg;
}

/*
 * builtin_cmd - If the user has typed a built-in command then execute
 *    it immediately.
 */
int builtin_cmd(char **argv, char *cmdline)
{
    char *first_arg = argv[0];

    if (first_arg == NULL) /* if input nothing('\n') in function main, then the
                              first_arg here will be NULL, which will cause SEG fault when invoke strcmp(read) */
    {
        return 1;
    }

    if (!strcmp(first_arg, "quit"))
    {
        exit(0);
    }
    else if (!strcmp(first_arg, "jobs"))
    {
        listjobs(jobs);
        return 1;
    }
    else if (!strcmp(first_arg, "bg") || !strcmp(first_arg, "fg"))
    {
        do_bgfg(argv, cmdline);
        return 1;
    }

    return 0;
}

/*
 * do_bgfg - Execute the builtin bg and fg commands
 */
void do_bgfg(char **argv, char *cmdline)
{
    char *first_arg = argv[0];
    if (!strcmp(first_arg, "bg"))
    {
        if (argv[1] == NULL)
        {
            fprintf(stderr, "bg command requires PID or %%jobid argument\n");
            return;
        }

        if (argv[1][0] == '%') /* JID */
        {
            int jid = atoi(argv[1] + 1);
            if (jid)
            {
                struct job_t *job_tmp = getjobjid(jobs, jid);
                if (job_tmp != NULL)
                {
                    job_tmp->state = BG;
                    printf("[%d] (%d) %s", jid, job_tmp->pid, job_tmp->cmdline);
                    stopped_resume_child = job_tmp->pid;
                    killpg(job_tmp->pid, SIGCONT);
                   
                    return;
                }
                else
                {
                    fprintf(stderr, "%%%s: No such job\n", argv[1] + 1);
                }
            }
            else
            {
                fprintf(stderr, "%%%s: No such job\n", argv[1] + 1);
            }
        }
        else /* PID */
        {
            pid_t pid = atoi(argv[1]);
            if(pid)
            {
                struct job_t *job_tmp = getjobpid(jobs, pid);
                if (job_tmp != NULL)
                {
                    job_tmp->state = BG;
                    printf("[%d] (%d) %s", job_tmp->jid, pid, job_tmp->cmdline);
                    stopped_resume_child = job_tmp->pid;
                    killpg(pid, SIGCONT);
                   
                    return;
                }
                else
                {
                    fprintf(stderr, "(%s): No such process\n", argv[1]);
                }
            }
            else
            {
                fprintf(stderr, "bg: argument must be a PID or %%jobid\n");
            }
        }
    }
    else
    {
        /* there are two case when using fg:
        1. the job stopped 
        2. the job is running
        */

        if (argv[1] == NULL)
        {
            fprintf(stderr, "fg command requires PID or %%jobid argument\n");
            return;
        }
        if (argv[1][0] == '%') /* JID */
        {
            int jid = atoi(argv[1] + 1);
            if (jid)
            {
                struct job_t *job_tmp = getjobjid(jobs, jid);
                if (job_tmp != NULL)
                {
                    int state = job_tmp->state;
                    fg_pid = job_tmp->pid; /* this is the new foreground process */
                    fg_pid_reap = 0;

                    job_tmp->state = FG;

                    if (state == ST)
                    {
                        stopped_resume_child = job_tmp->pid; /* set the global var in case of wait in SIGCHLD handler */
                        killpg(job_tmp->pid, SIGCONT);
                    }
                    
                    waitfg(job_tmp->pid); /* wait until the foreground terminate/stop */
                    return;
                }
                else
                {
                    fprintf(stderr, "%%%s: No such job\n", argv[1] + 1);
                }
            }
            else
            {
                fprintf(stderr, "%%%s: No such job\n", argv[1] + 1);
            }
        }
        else /* PID */
        {
            pid_t pid = atoi(argv[1]);
            if(pid)
            {
                struct job_t *job_tmp = getjobpid(jobs, pid);
                if (job_tmp != NULL)
                {
                    int state = job_tmp->state;
                    fg_pid = job_tmp->pid; /* this is the new foreground process */
                    fg_pid_reap = 0;

                    job_tmp->state = FG;

                    if (state == ST)
                    {
                        stopped_resume_child = job_tmp->pid; /* set the global var in case of wait in SIGCHLD handler */
                        killpg(pid, SIGCONT);
                    }
                    
                    waitfg(job_tmp->pid); /* wait until the foreground terminate/stop */
                    return;
                }
                else
                {
                    fprintf(stderr, "(%s): No such process\n", argv[1]);
                }
            }
            else
            {
                fprintf(stderr, "fg: argument must be a PID or %%jobid\n");
            }
        }
    }
    return;
}

/*
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{
    while (!fg_pid_reap)
    {
        sleep(1);
    }
    fg_pid_reap = 0;
    return;
}

/*****************
 * Signal handlers
 *****************/

/*
 * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
 *     a child job terminates (becomes a zombie), or stops because it
 *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
 *     available zombie children, but doesn't wait for any other
 *     currently running children to terminate.
 */
void sigchld_handler(int sig) /* When a child process stops or terminates, SIGCHLD is sent to the parent process. */
{
    int olderrno = errno;

    if (stopped_resume_child)
    {
        stopped_resume_child = 0;
        return;
    }
    int status;
    pid_t pid;

    if ((pid = waitpid(-1, &status, WUNTRACED)) > 0) /* don't use while! */
    {
        if (pid == fg_pid)
        {
            fg_pid_reap = 1;
        }

        if (WIFEXITED(status)) /* returns true if the child terminated normally */
        {
        
        
            deletejob(jobs, pid);
        }
        else if (WIFSIGNALED(status)) /* returns true if the child process was terminated by a signal. */
                                      /* since job start from zero, we add it one */
        {
        
        
            printf("Job [%d] (%d) terminated by signal %d\n", pid2jid(pid), pid, WTERMSIG(status));
            deletejob(jobs, pid);
        }
        else /* SIGTSTP */
        {
            /* don't delete job */
            struct job_t *p = getjobpid(jobs, pid);
            p->state = ST; /* Stopped */
            printf("Job [%d] (%d) stopped by signal 20\n", pid2jid(pid), pid);
        }
    }

    errno = olderrno;
    return;
}

/*
 * sigint_handler - The kernel sends a SIGINT to the shell whenver the
 *    user types ctrl-c at the keyboard.  Catch it and send it along
 *    to the foreground job.
 */
void sigint_handler(int sig)
{
    int olderrno = errno;

    pid_t pgid = fgpid(jobs);
    if (pgid)
    {
        killpg(pgid, SIGINT);
    }

    errno = olderrno;
    return;
}

/*
 * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
 *     the user types ctrl-z at the keyboard. Catch it and suspend the
 *     foreground job by sending it a SIGTSTP.
 */
void sigtstp_handler(int sig)
{
    int olderrno = errno;

    pid_t pgid = fgpid(jobs);
    if (pgid)
    {
        killpg(pgid, SIGTSTP);
    }
    
    errno = olderrno;
    return;
}

/*********************
 * End signal handlers
 *********************/

/***********************************************
 * Helper routines that manipulate the job list
 **********************************************/

/* clearjob - Clear the entries in a job struct */
void clearjob(struct job_t *job) {
    job->pid = 0;
    job->jid = 0;
    job->state = UNDEF;
    job->cmdline[0] = '\0';
}

/* initjobs - Initialize the job list */
void initjobs(struct job_t *jobs) {
    int i;

    for (i = 0; i < MAXJOBS; i++)
    clearjob(&jobs[i]);
}

/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs)
{
    int i, max=0;

    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].jid > max)
        max = jobs[i].jid;
    return max;
}

/* addjob - Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
{
    int i;

    if (pid < 1)
    return 0;

    for (i = 0; i < MAXJOBS; i++) {
    if (jobs[i].pid == 0) {
        jobs[i].pid = pid;
        jobs[i].state = state;
        jobs[i].jid = nextjid++;
        if (nextjid > MAXJOBS)
        nextjid = 1;
        strcpy(jobs[i].cmdline, cmdline);
        if(verbose){
            printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
            }
            return 1;
    }
    }
    printf("Tried to create too many jobs\n");
    return 0;
}

/* deletejob - Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid)
{
    int i;

    if (pid < 1)
    return 0;

    for (i = 0; i < MAXJOBS; i++) {
    if (jobs[i].pid == pid) {
        clearjob(&jobs[i]);
        nextjid = maxjid(jobs)+1;
        return 1;
    }
    }
    return 0;
}

/* fgpid - Return PID of current foreground job, 0 if no such job */
pid_t fgpid(struct job_t *jobs) {
    int i;

    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].state == FG)
        return jobs[i].pid;
    return 0;
}

/* getjobpid  - Find a job (by PID) on the job list */
struct job_t *getjobpid(struct job_t *jobs, pid_t pid) {
    int i;

    if (pid < 1)
    return NULL;
    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].pid == pid)
        return &jobs[i];
    return NULL;
}

/* getjobjid  - Find a job (by JID) on the job list */
struct job_t *getjobjid(struct job_t *jobs, int jid)
{
    int i;

    if (jid < 1)
    return NULL;
    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].jid == jid)
        return &jobs[i];
    return NULL;
}

/* pid2jid - Map process ID to job ID */
int pid2jid(pid_t pid)
{
    int i;

    if (pid < 1)
    return 0;
    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].pid == pid) {
            return jobs[i].jid;
        }
    return 0;
}

/* listjobs - Print the job list */
void listjobs(struct job_t *jobs)
{
    int i;

    for (i = 0; i < MAXJOBS; i++) {
    if (jobs[i].pid != 0) {
        printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
        switch (jobs[i].state) {
        case BG:
            printf("Running ");
            break;
        case FG:
            printf("Foreground ");
            break;
        case ST:
            printf("Stopped ");
            break;
        default:
            printf("listjobs: Internal error: job[%d].state=%d ",
               i, jobs[i].state);
        }
        printf("%s", jobs[i].cmdline);
    }
    }
}
/******************************
 * end job list helper routines
 ******************************/


/***********************
 * Other helper routines
 ***********************/

/*
 * usage - print a help message
 */
void usage(void)
{
    printf("Usage: shell [-hvp]\n");
    printf("   -h   print this message\n");
    printf("   -v   print additional diagnostic information\n");
    printf("   -p   do not emit a command prompt\n");
    exit(1);
}

/*
 * unix_error - unix-style error routine
 */
void unix_error(char *msg)
{
    fprintf(stdout, "%s: %s\n", msg, strerror(errno));
    exit(1);
}

/*
 * app_error - application-style error routine
 */
void app_error(char *msg)
{
    fprintf(stdout, "%s\n", msg);
    exit(1);
}

/*
 * Signal - wrapper for the sigaction function
 */
handler_t *Signal(int signum, handler_t *handler)
{
    struct sigaction action, old_action;

    action.sa_handler = handler;
    sigemptyset(&action.sa_mask); /* block sigs of type being handled */
    action.sa_flags = SA_RESTART; /* restart syscalls if possible */

    if (sigaction(signum, &action, &old_action) < 0)
    unix_error("Signal error");
    return (old_action.sa_handler);
}

/*
 * sigquit_handler - The driver program can gracefully terminate the
 *    child shell by sending it a SIGQUIT signal.
 */
void sigquit_handler(int sig)
{
    printf("Terminating after receipt of SIGQUIT signal\n");
    exit(1);
}